Impacts of ocean acidity feed oyster grower’s research

David Briggs

By

Jacoba Charles

05/30/2013

A handful of what looks like damp, grayish cereal sits in a plastic tub on Hog Island Oyster Company owner Terry Sawyer’s desk. It looks like small cornflakes, or maybe cooked quinoa. But actually these are spat: many hundreds of tiny “seed” oysters, each barely a millimeter wide. The hope is that each spat will grow into a tasty treat on the half-shell—but most of this batch is already dead.

Like many terrestrial farmers, Mr. Sawyer buys his seed from distributors. In recent years, however, it has become harder to get and harder to grow. Since 2006, West Coast oyster hatcheries have suffered catastrophic collapses, which have led to widespread shortages. The reason? Ocean acidification, a phenomenon that many call the evil twin of climate change.

“This has huge impacts, from recreation to food to ecology,” Mr. Sawyer said. “It is everybody’s problem, but in this industry we find ourselves on the front line because we are growing the food.”

Because of the shortages in healthy spat, Mr. Sawyer has had to be inventive to keep up with demand. For the busy Memorial Day weekend he trucked in extra bivalves to feed the holiday crowd.

He also has started to buy his stock at an earlier age—setting smaller seed, or even free-floating larvae only a few days old—in the hopes of achieving a better survival rate.

Hog Island is working toward opening its own hatchery in Humboldt Bay. It’s an aspect of the business Mr. Sawyer and his partner, John Finger, never planned to get into, but with the few existing hatcheries struggling to meet demand, it’s the only way to ensure a constant supply for the steady stream of customers flocking to the farm and the company’s oyster bars in San Francisco and Napa.

The oyster farm has also partnered with scientists with the University of California, Davis Bodega Marine Lab, the California Current Acidification Network, and the Central and Northern California Ocean Observing System.

Last year, Mr. Sawyer collaborated with the Bodega Marine Lab to install sensors at the mouth of the farm’s seawater intake pipes. These moored instruments monitor daily changes in temperature, salinity, oxygen and pH.

“We’re using the data to try to address big picture questions,” said Dr. Tessa Hill, who is heading up the project. “Terry and others in aquaculture have been real leaders at standing up and saying, ‘This is a problem and we have to do something about it.’”

Seeds of change
Ocean acidification has been in the news for well over a decade as one of the causes of coral reef collapse. But it wasn’t until last year that it was fingered as the reason for increasing challenges in the oyster trade.

“The oyster industry tells us that every hatchery [on the West Coast] is being affected,” Dr. Burke Hales of Oregon State University, co-author of last year’s study, said. “The stories they tell me are pretty extreme.”

The problems began in 2006, upsetting what had been a stable industry since it first formed in the 1970s. Once disease, low oxygen and other possible causes were ruled out, hatcheries and scientists began to zero in on ocean acidification.

The world’s oceans are like giant sponges, soaking up atmospheric carbon dioxide. The more we pump out, the more they soak up.

The gas reacts with water, resulting in higher overall acidity. At the same time, this chemical reaction uses up the carbonate ions that many sea creatures need to build their calcium carbonate shells. The result is a double whammy, creating a corrosive environment in which it is harder for oysters to both grow and maintain shells.

“A baby oyster is trying to eat, grow, move around and make a shell. So if it spends more energy trying to make a shell then something else in that equation is going to suffer,” Dr. Hill said. “I say it’s like balancing your checkbook—you can’t spend a lot of energy on one thing without cutting back in some other category.”

Right now, the days of dangerously high acidity are sporadic. If a larval oyster is exposed during the first 24 hours of its life, it will either be killed outright or suffer a long-lasting decrease in vigor. Now that hatcheries know what the problem is, they are responding by simply not spawning new oysters when conditions are bad.

But by 2030, bad conditions are expected to last most of the summer in California, according to an article published in Science last year. And by 2050, they are expected to last year-round in many places.

What’s gone wrong?
From the shore, the sea can seem grand and unchanging: a unified mass beneath the onslaught of weather and the surface tumult of waves.

But it turns out that the chemistry of the water is constantly changing—especially in estuaries like Tomales Bay. Currents play a part, as do daily shifts in salinity as the tides change the balance of fresh and salt water. Winter runoff and human pollution add to the mix. Even sunlight has an impact—when water plants are photosynthesizing and absorbing carbon dioxide from the water, acidity temporarily declines.

But buried in all of these changes is a historical average, or baseline, of acidity that is constantly creeping upwards. “The really big ups and downs in the cycle are natural, but now the bad conditions are worse,” Dr. Hales said.

Since the first industrial revolution ended over 150 years ago, humans have released over 440 billion metric tons of carbon dioxide into the atmosphere; half of that has come in the last three decades. And about a third of those emissions have been soaked up by the oceans.

The result is that marine life hasn’t seen water this corrosive in 20 million years—and there has never been a change that happened as fast. Oceans are taking up carbon dioxide about 100 times faster than it was at the end of the last glacial period, 20,000 years ago.

Making matters worse, the West Coast is one of the first places where changes in ocean acidity show up because of wind and current patterns. A slow cycling of water called upwelling brings decades-old water to the surface along our shores.

Upwelled water is always acidic—while it lingers deep in the ocean interior it absorbs the carbon dioxide from everything that sinks and decomposes there. But the upwelling we see now carries the added legacy of carbon dioxide absorbed from the air during the 1960s or 1970s when greenhouse gasses were already elevated, but were still much lower than they are today.

As today’s surface water is being pulled under to take its own place in the cycle, it will return to us decades later bearing even higher levels of acidity.

“We’re definitely playing the role of canary in the coal mine,” Dr. Hales said. “But, it’s also one of those things that’s hard to stop. The problem won’t be solved if everybody goes and buys a Prius. This is something that’s global in extent and takes generations to reverse.”

Ecological ripples
Without a major change in fossil fuel emissions, a child exploring the rocky shoreline of Tomales Bay 50 years from now is likely to see a very different ecosystem than the one here today, Dr. Hill says. Her lab studies how Olympic oysters and other native species fare under the ocean conditions predicted for the near future.

Crabs, lobsters and sea urchins might be just fine, she says, but oysters and mussels will definitely suffer. As acidity goes up, many either die or grow to smaller sizes and have thinner shells more vulnerable to crashing waves and the powerful claws of hungry crabs.

The mussels that play such an important structural role in the intertidal zone—building reefs of shells where other organisms live and feed—appear to be the most dramatically impacted.

Oysters and mussels are a foundation of the food chain. They reproduce by spewing millions of tiny larvae out into the open ocean. As they float and grow, waiting for the right moment to stick on to a rock, they are food for fish and other filter feeders. As fewer survive, less food will work its way up the food chain. Fewer adults will survive to feed otters, seals, crabs and other predators. And fewer still will survive long enough to produce the next generation.

It is not that the seashore will become a wasteland, but that it will change in ways that can’t be predicted and could be dramatic. “Not everything will be a loser,” Dr. Hill said, adding that some species likely won’t respond at all, and some—those that don’t require calcium carbonate—might respond in a positive way.

Meanwhile, she and other researchers have nearly 50 research sites up and down the coast where they are trying to figure out if there are areas that will be less affected and could serve as natural refuges. They also are investigating small-scale places or environments that might offer localized protection against rising acidity. For example, eelgrass beds might buffer the effect for a while.

In the long term, scientists agree that the only way to moderate future changes is to make some ourselves.

“The only way to stop the course that we are on is to stop using carbon based fuels,” Dr. Hill said. “There is no other course of action.”